The present invention relates to a frame for a water-jet propulsion unit, which is arranged to be installed and sealed into an installation opening for a water-jet propulsion unit belonging to a boat, which frame includes                a flow channel for guiding water to the impeller belonging to the water-jet propulsion unit,        a maintenance opening located on top of the flow channel, for servicing the impeller, and        a sealing surface forming a closed loop for attaching the water-jet propulsion unit tightly to a counter-sealing surface belonging to the boat.        
The invention also relates to a corresponding water-jet unit equipped with a water-jet propulsion unit's frame, and an arrangement in a boat.
Water-jet propulsion units suck the water required for the water jet into a flow channel, in which the velocity of the water is increased with the aid of an impeller. Water-jet propulsion units are situated in such a way that the flow channel is located entirely or at least partially outside the boat. Garbage can easily enter the flow channel and wind itself around the impeller or other parts. For this reason, a separate maintenance opening, through which maintenance can be performed, is required for servicing the impeller and flow channel of the water-jet propulsion unit.
According to the wishes of customers, water-jet propulsion units are attached to a boat equipped with an attachment opening, in such a way that the maintenance opening is located either inside or outside the stern of the boat. A maintenance opening located inside facilitates maintenance directly from the boat, but on the other hand causes the risk of a leak if the maintenance opening leaks. A maintenance opening located outside does not have the risk of a leak, but on the other hand makes maintenance difficult to perform outside the stern of the boat. Publication U.S. Pat. No. 5,522,742 A discloses a boat, in which the water-jet propulsion unit is installed in such a way that the maintenance opening is situated inside the stern.
Due to the various ways of installing water-jet propulsion units, each form of installation requires a separate structure, either in the frame of the water-jet propulsion unit or in the boat. This, in turn, demands two separate models, depending on the manner of installation, from the manufacturers of the water-jet propulsion units or of boats or of both, which leads to increasing design costs.